Electron Paramagnetic Resonance Study of Potassium Di-Hydrogen Phosphate Doped with Cr³⁺ Ions

EPR spectra of KDP (KH 2 PO 4 ):Cr 3+ have been studied to reveal mech-anism of the ferroelectric and ferroelectric phase transition. There are two kinds of Cr 3+ ion sites in the para phase and these sites are divided into two slightly different kinds of sites in the ferro phase which reflects the domain structure. An EPR sample holder with a uniaxial stress squeezer is designed; the domain switching by electric field and by uniaxial stress is observed. The Cr 3+ ions of site I substitutionally take the position of K + ions and the spin Hamiltonian parameters are g X = g Y = g Z =1.97, | D |=0.455 cm -1 , | E |=0.143 cm -1 , and D · E >0. The transition at site I is related to the second-order transition, on the other hand, the one at site II, the first-order transition. Therefore the first and second order transitions, which are anharmonically coupled to each other, are there. Dielectric, thermal and optical properties are also studied.